To facilitate assembly, maintenance and/or repair of bearing assemblies, it is advantageous to secure the bearing races to the respective mating elements with a minimum degree of structural complexity. For example, a bearing race which must be press fit over a connecting pin or shaft is more difficult and costly to assemble/maintain than one which employs a simple structural interlock, e.g., a slot and key arrangement, to effect the necessary engagement. Furthermore, to prevent fretting or chaffing between elements, it is desirable to minimize or essentially negate relative motion between the bearing race and its mating element. That is, fretting wear is minimized by a structural interlock which causes the bearing race and the respective mating element to move as a unitary component.
Prior art bearing assemblies employ various structural interlocks which rely on friction, mechanical interference or some combination thereof. For example, it is common practice to rely on an axial clamp-up force to generate sufficient friction between a bearing and its mating element to counteract motion induced by torque. For applications wherein sufficient friction cannot be induced, the structural interlock may be effected by mechanical interference such as mating flats to rotationally couple the bearing race to its mating element. While this arrangement provides structural simplicity, machining and/or manufacturing tolerances produce an imperfect fit which can produce fretting.
A structural interlock which employs both friction and mechanical interference is depicted in FIG. 1a. More specifically, FIG. 1a depicts an elastomeric bearing 100 for accommodating relative motion between first and second elements 104 and 106, respectively, about an axis of rotation 108. The elastomeric bearing 100 is conventional and comprises an inner race 110, an outer race 112 and a plurality of alternating layers of elastomer and non-resilient metallic shims, 114 and 116, respectively. The inner race 110 is disposed about a connecting pin 118 which mounts between a pair of lugs 120 of the first element 104, and the outer race 112 is integrally formed in combination with the second element 106. More specifically, the inner race 110 is rotationally fixed relative to the lugs 120 by means of a structural interlock 124 formed between an end face 110.sub.F of the inner race 110 and a press fit bushing 128 of one of the lugs 120.
In FIGS. 1a and 1b, the structural interlock 124 comprises serrate teeth 130 forming the end face 110.sub.F of the inner race 110 which serrate teeth 130 engage the bushing 128 upon clamp-up of the connecting pin 118. That is, the serrate teeth 130, which comprise a harder material than the bushing 128, plastically deform the bushing 128 upon application of an axial clamp-up force P. As such, a mechanical and frictional interlock is produced to prevent relative rotation between the inner race 110 of the elastomeric bearing 102 and the lugs 120, and, consequently, between the inner race 110 and the connecting pin 118. Accordingly, the inner race 110 is held stationary with respect to the connecting pin 118 so as to abate fretting wear.
While the structural interlock 124 described above is readily fabricated and facilitates assembly, the serrate teeth 130 plastically deform the bushing 128 such that it must be replaced following each event of repair/maintenance, e.g., disassembly of the clevis joint 100 or replacement of the elastomeric bearing 102. While such disposal is typically deemed acceptable due to the relatively low cost of conventional bushings, more recently, it is desirable to employ cold-worked bushings which produce beneficial fatigue effects. More specifically, such cold-worked bushings are initially undersized relative to its receiving aperture and radially expanded or cold-worked into the aperture. Such cold-working produces residual stresses which improve the strength and fatigue life of the bushing/aperture.
In view of this installation procedure, it will be appreciated that such bushings are not intended for applications requiring frequent replacement. For example, each time a bushing is replaced rework of the aperture will be required. Furthermore, a slightly larger bushing will be required relative to the bushing it replaced. Accordingly, in addition to rework operations, a multiplicity of bushings must be held in inventory to ensure that the proper size bushing is available for replacement.
A need, therefore, exists for a structural interlock which inhibits relative rotation between mating elements while providing structural simplicity for ease of assembly, repair and/or maintenance.